`AllOk` runs a set of promises concurrently, and like `TryJoin` waits for them all to succeed or one to fail.
Unlike `TryJoin` it returns a single unified status of the composition, so cannot handle member promises that might return `StatusOr` or the like.
Closes#35304
Our current implementation of Join, TryJoin leverage some complicated
template stuff to work, which makes them hard to maintain. I've been
thinking about ways to simplify that for some time and had something
like this in mind - using a code generator that's at least a little more
understandable to code generate most of the complexity into a file that
is checkable.
Concurrently - I have a cool optimization in mind - but it requires that
we can move promises after polling, which is a contract change. I'm
going to work through the set of primitives we have in the coming weeks
and change that contract to enable the optimization.
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Co-authored-by: ctiller <ctiller@users.noreply.github.com>
Craig Tiller